Outbred (Swiss) and genetically and behaviorally defined strains of MICE will be inoculated extraneurally with MOUSE CYTOMEGALOVIRUS (MCMV), and their brains studied periodically thereafter for content and localization of virus and the nature of histologic change induced. The effects of prior maternal IMMUNIZATION on these processes will be studied by assessing the protection afforded by diaplacentally acquired factors and those obtained by nursing. Humoral and cellular immune factors in blood and breast milk will be studied. After the acute phase the behavior of the mice will be studied to determine whether there are changes associated with these virologic and neuropathologic changes in the CENTRAL NERVOUS SYSTEM (CNS). This information is being sought in the hope that it might be used to ameliorate or prevent CNS damage and dysfunction including MENTAL RETARDATION caused in human beings by HUMAN CYTOMEGALOVIRUS.